In the past, a control system of an internal combustion engine provided with a means for calculating the amount of change of cylinder pressure between immediately after closing of the intake valve and immediately before ignition based on a cylinder pressure, crank angle, and throttle opening degree and a means for calculating the amount of intake air from the amount of change of the cylinder pressure and an engine speed has been known (for example, see Japanese Patent Publication (A) No. 2-40054). Further, in the past, an internal combustion engine able to set valve overlap for making an intake valve and exhaust valve simultaneously open for improving the output or efficiency and reducing emissions has been known in the past. Further, as this type of internal combustion engine, an engine provided with a control system able to calculate the amount of gas remaining in a combustion chamber (amount of internal EGR) due to the valve overlap between the intake valve and exhaust valve has been known (for example, see Japanese Patent Publication (A) No. 2004-108262).
The control system described in Japanese Patent Publication (A) No. 2004-108262 calculates the cylinder temperature and cylinder pressure based on signals from an exhaust temperature sensor, intake pressure sensor, and exhaust pressure sensor at the time of closing of the exhaust valve, calculates the gas constant of the exhaust gas in accordance with the burned air-fuel ratio, and calculates the amount of cylinder gas at the time of closing of the exhaust valve based on the cylinder temperature, cylinder pressure, and gas constant. Further, this control system calculates the amount of blowback gas during overlap between the intake valve and exhaust valve based on signals from a crank angle sensor, water temperature sensor, cam angle sensor, and accelerator opening degree sensor and calculates the amount of gas remaining in a combustion chamber (amount of internal EGR) due to the valve overlap based on the amount of cylinder gas and the amount of blowback gas.